With the development of Internet technologies, communication among accounts becomes increasingly popular. On a social network platform, a user can exchange messages with another user or a group of users in substantially real time. The messages can be in textual or voice form. In addition to natural language messages, the users may also exchange media items, such as videos, pictures, files, etc. On a social network platform, a user may add one or more accounts of other users or public entities (e.g., weather services, traffic information services, taxi calling services, celebrities, government agencies, etc.) as his/her social network contacts, and exchange messages with these social network contacts.